How to check if Python app is running within AWS lambda function?
EDIT 2: Thanks @MarkB for the update regarding the new feature of custom runtimes.
The Approach: There are certain environment variables whose value is set when code runs in AWS. Checking for the existence of such variables would indicate that the code is running in AWS.
However, due to a new feature my previous take on it with AWS_EXECUTION_ENV environment variable does not work in all cases. From the docs here https://docs.aws.amazon.com/lambda/latest/dg/configuration-envvars.html The AWS_EXECUTION_ENV environment variable is not defined for custom runtimes, which means that checking for its existence when using custom runtimes would not be an indicator of whether the code is running on AWS.
One can check for the existence of one of the other AWS_* specific environment variables (see link above). Which one is right for you might depend on your use case. But Mark's suggestion looks good!
os.environ.get("AWS_LAMBDA_FUNCTION_NAME") is not None
This works for me The following would work as long as you are using a standard AWS runtime environment
os.environ.get("AWS_EXECUTION_ENV") is not None
EDIT: I find the existence of the context object insufficient for such a check because you might be mocking it when not running within an AWS lambda function. Then again, you may be mocking the AWS_EXECUTION_ENV as well ...
EDIT 2: With the introduction of Lambda function custom runtimes, it may be better to check for the AWS_LAMBDA_FUNCTION_NAME environment variable, like so:
os.environ.get("AWS_LAMBDA_FUNCTION_NAME") is not None
EDIT: See the other answer, this is a better solution:
os.environ.get("AWS_EXECUTION_ENV") is not None
Original answer:
How about checking for the existence of the context object in the handler function? http://docs.aws.amazon.com/lambda/latest/dg/python-programming-model-handler-types.html